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RADIATION PROTECTION IN DIAGNOSTIC AND INTERVENTIONAL RADIOLOGY

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Title: RADIATION PROTECTION IN DIAGNOSTIC AND INTERVENTIONAL RADIOLOGY


1
RADIATION PROTECTION INDIAGNOSTIC
ANDINTERVENTIONAL RADIOLOGY
IAEA Training Material on Radiation Protection in
Diagnostic and Interventional Radiology
  • L15.2 Optimization of protection in radiography
    Radioprotection aspects

2
Introduction
  • Optimization of patient radiation protection
    requires periodic evaluation of doses and image
    quality.
  • Operators of the X Ray system should be aware of
    the interdependence between technical parameters,
    dose and image quality
  • Procedures should be established for each
    examination to ensure a proper use of equipment.

3
Topics
  • Practical rules to protect patients
  • Generators and X Ray production related
    parameters
  • Imaging devices related parameters (film,
    intensifying screens)
  • Examination procedures related parameters (number
    of radiographic projections, technical settings..)

4
Part 15.2 Optimization of protection in
radiography
IAEA Training Material on Radiation Protection in
Diagnostic and Interventional Radiology
  • Topic 1 Practical rules to protect patients

5
Existing past images
  • Before beginning an examination, it is advisable
    to compile the existing past images of similar
    examinations in or outside the institution, in
    order to minimize the number of radiological
    examinations that the patient has to bear.

6
Periodic measurement of the entrance patient dose
  • The periodic measurement (at least once a year)
    of the entrance patient dose (or similar
    quantity) and the comparison with the guidance
    (or reference) levels and with values from
    previous controls will permit the detection of
    equipment malfunctions
  • When the entrance doses (or other dosimetric
    parameters) are clearly in excess of the guidance
    levels (or of those previously obtained), it is
    necessary to check the generator and associated
    devices, as well as the procedures and techniques
    used for the examination.

7
Periodic evaluation of the image quality
  • A periodic evaluation (at least once a year) of
    the image quality obtained in each room allows
    the detection of malfunctioning in the imaging
    chain or in the generator (almost always
    associated to high patient doses and poor image
    quality)
  • A periodic evaluation of the number of rejected
    and repeated radiographs and the analysis of the
    causes of rejects and retakes allow the detection
    of failures in the X Ray equipment, associated
    image devices, as well as in the examination
    procedures and in the skill and training of the
    staff

8
Corrective actions
  • When some corrective measures are proposed after
    the detection of a malfunctioning, recording the
    follow up of their implementation is advisable
    (in a logbook)
  • On the contrary, most of them will not be carried
    out.

9
Skin focus distance and others
  • In general radiography (except dental) and
    fluoroscopy with X Ray mobile equipment, the
    skin-focus distance should not be lower than 30
    cm
  • In radiography and fluoroscopy with fixed
    equipment, the skin-focus distance should not be
    lower than 45 cm
  • The fluoroscopy equipment without image
    intensifiers must be replaced, or upgraded with
    an image intensifier

10
Practical rules to protect patients
  • When there are suspicions about a malfunctioning
    of the X Ray unit or of the imaging chain in a
    room that might affect the protection of the
    patient (i.e., because the images become over or
    underexposed without changing the technique),
    this should be reported to the responsible of the
    room in order to reevaluate the equipment if
    necessary and to introduce corrective actions.

11
Part 15.2 Optimization of protection in
radiography
IAEA Training Material on Radiation Protection in
Diagnostic and Interventional Radiology
  • Topic 2 Generators and X Ray productionrelated
    parameters

12
With reference to generators and X Ray tubes
filtration
  • Whether imported into or manufactured in the
    country where it is used, the equipment should
    conform to applicable standards of the
    International Electrotechnical Commission (IEC)
    and the ISO or to equivalent national standards
  • A correct filtration (minimum 2.5 mm Al, in
    general radiology), significantly reduces the
    patient dose due to low energy X Rays which do
    not contribute to the image formation
  • In tubes equipped with removable aluminum filters
    (added filtration), it is important to verify
    whether they are still in place after any
    possible maintenance or repairing of X Ray tube

13
With reference to generators and X Ray tubes (I)
  • In tubes in which filters are not accessible
    neither visible from the outside, it is advisable
    to verify, at least once in the tube lifetime,
    that the correct filtration is in place. After
    each repairing or maintenance during which the
    tube housing is removed, a certificate should be
    obtained proving that filters have been restored
  • In mammography, very low voltages are used and
    the filtration requirements are different (0.03
    mm thickness of Molybdenum recommended, in
    equipment with anode of the same material).

14
With reference to generators and X Ray tubes (II)
  • In examinations with fluoroscopy, a clock should
    be available allowing the measurement of the
    fluoroscopy elapsed time, with audible
    indications at 10 or 5 minutes.
  • Fluoroscopy should be controlled with a switch of
    a "dead man" type.

15
With reference to generators and X Ray tubes (III)
  •  When using mobile equipment in intensive care
    units, in patient rooms or in other different
    locations such as general diagnostic radiology
    rooms, one must not forget that generators
    require a high instantaneous electric power
    supply
  • A too low power supply will affect image quality.

16
With reference to generators and X Ray tubes (IV)
  • For the same reason, in order to avoid retakes,
    it is very important to guarantee that the
    battery attached to the equipment is properly
    charged
  • For units connected to the mains, one must be
    sure that the required power is actually supplied.

17
Part 15.2 Optimization of protection in
radiography
IAEA Training Material on Radiation Protection in
Diagnostic and Interventional Radiology
  • Topic 3 Imaging devices related parameters

18
With reference to imaging devices screen-film
combination
  • The use of the appropriate screen-film
    combination, the "fastest" compatible with the
    type of image that is looked for, is recommended
    to guarantee the lowest patient dose
  • Due to human errors, it is not advisable to use
    in the same room, several screen-film
    combinations of different sensitivity class
  • An exception is the case when each combination
    has a different film format and the selection of
    radiological technique is made manually (no AEC)  

19
With reference to imaging devices (I)
  • The use of cassettes, grid holders and tables of
    carbon fiber material, results in important
    patient dose reductions
  • The use of intensifying screens with, scratches,
    or cassettes that do not provide the correct
    film-screen contact should be avoided

20
With reference to imaging devices automatic
exposure control
  • Inappropriate selection of automatic exposure
    control settings might lead to incorrectly
    contrasted images (too dark or too clear).
  • Then the automatic exposure control device should
    ALWAYS be checked, in particular when the
    sensitivity of the screen-film combination has
    been changed.
  • The correct operation of the automatic exposure
    control device requires, for each projection, the
    selection of the chamber or detector closer to
    the area of interest, so that this area be best
    contrasted.

21
With reference to imaging devices (II)
  • The patient entrance air kerma rate should not
    usually exceed 50 mGy/min.
  • In modern image intensifiers, this value should
    be much lower depending on patient size and
    projection
  • The use of devices for memorizing the last image
    (last image hold) is recommended

22
With reference to imaging devices (III)
  • In either automatic or manual processors, it is
    essential to change the chemicals according to
    the manufacturer instructions, with respect to
    both the expiration time and the number of
    processed films.
  • The safelights in darkrooms do not have filters
    with endless life. Replacement is recommendable
    at least once a year (twice a year is optimal).
  • When changing to a more sensitive film than the
    former used, it might be advisable to reduce the
    safelight power (or change filters) in the
    darkroom.

23
With reference to imaging devices (IV)
  • It is very important to have viewing boxes in
    areas with correct environmental light, enough
    brightness and uniformity over the surface and,
    for certain applications (e.g. mammography)
    complementary high intensity light sources.
    Hence, periodic cleaning of the internal and
    external surfaces and replacement of the
    fluorescent tubes are essential
  • Make sure that the illuminated area coincides
    with the radiograph size, so that diaphragmable
    viewing boxes are recommended

24
Part 15.2 Optimization of protection in
radiography
IAEA Training Material on Radiation Protection in
Diagnostic and Interventional Radiology
  • Topic 4 Examination procedures related
    parameters

25
With reference to procedures (I)
  • The usual radiological technique for each
    projection on a given equipment, with details of
    the associated image device should be written and
    be readily accessible, close to the control
    panel. It should be specified for patients of
    standard as well as uncommon size
  • Thus any personnel (substitutes, night personnel
    or staff after time periods of a different work
    different examinations or work in another room)
    would know those techniques without having to
    resort to "estimates" and retakes 

26
With reference to procedures (II)
  • With any equipment (manually as well as
    automatically controlled), it is important to
    know which set of parameters (technique) are to
    be selected to obtain a good image
  • When changes are introduced on whichever element
    of the imaging chain (generator or tube as well
    as other accessory devices such as film type,
    cassette, intensifying screen, etc), an update of
    technical settings should be performed
  • A yearly check of those updates is also advisable

27
With reference to procedures (III)
  • It is advisable to use the highest kVp (and the
    lowest mAs) compatible with the image that one
    expects to obtain. In this way the patient
    irradiation will be lower, although it might get
    lower image contrast. Therefore the optimization
    is to find the proper balance between contrast
    and dose
  • The shortest exposure time as possible should be
    selected, above all when examining non-
    collaborating patients (shorter time means
    reduction in kinetic blurring)

28
With reference to procedures (IV)
  • Hence, it is recommended to perform the pediatric
    examinations with generators (three-phase or high
    frequency, usually) capable of producing very
    short exposures, in order to avoid retakes due to
    the kinetic blurring and poor image quality
  • The radiographic techniques in use in each room
    should be compared on a regular basis with those
    recommended in published guidelines (EEC,BSS)

29
With reference to procedures (v)
  • Any radiological examination is assumed to have
    been prescribed by a properly accredited
    physician
  • When applicable, patients own record as well as
    medical indications that make recommendable the
    radiological examination should be available
    (WHO, EC)
  • Then it might be convenient to modify the
    examination procedure (e.g. to substitute it by
    another examination or to revoke it and contact
    the prescriber), in order to adopt the most
    appropriate strategy

30
With reference to procedures (VI)
  •  It is of extreme importance that the personnel
    operating the equipment is properly trained and
    accredited in radiation protection
  • Training criteria shall be specified or be
    subject to approval, as appropriate, by the
    Regulatory Authority in consultation with
    relevant professional bodies
  • The personnel should inform the patient on the
    correct positioning and immobilization as well as
    on technical prerequisites of the examination
    (suspended respiration, deep inspiration, etc)

31
With reference to procedures (VII)
  • It is important to ensure that the radiological
    examination is "justified", taking into account
    the benefits and risks of available alternative
    techniques that do not involve medical exposure
  • The patient should wear gonadal protectors, if
    gonads are exposed, assuming that it does not
    interfere with the expected image
  • In case of possible foetus irradiation it is
    advisable to adapt the examination procedure of
    pregnant women, together with the radiation
    protection strategy

32
With reference to procedures (VIII)
  • For that reason, in order to avoid unwanted
    irradiation of the fetus, it is recommended to
    post warnings, both at the X Ray room entrance
    and in the waiting ward such as

"IF YOU THINK THERE IS ANY POSSIBILITY THAT YOU
ARE PREGNANT, PLEASE TELL IT TO THE RADIOGRAPHER
(RADIOLOGICAL TECHNOLOGIST) OR THE RADIOLOGIST,
BEFORE THE X RAY EXAMINATION IS PERFORMED".
33
With reference to procedures (IX)
  • It should be asked to the female patient about
    the possibility of being pregnant, even to the
    pediatric patient in puberty. In the affirmative
    case appropriate measures should be taken
  • When a pregnant patient undergoes a radiological
    examination (in the abdomen), it might be
    advisable to make an individual evaluation of the
    expected fetus dose.

34
With reference to procedures (X)
  • The pregnant patient or worker has a right to
    know the magnitude and type of potential
    radiation effects that might result from in utero
    exposure
  • Communication should be related to the level of
    risk. Verbal communication may be adequate for
    low dose procedures
  • If fetal doses are above 1 mGy, usually a more
    detailed explanation is given

35
Approximate fetal doses from conventional X Ray
examinations (data from the UK 1998)
36
Approximate fetal doses from fluoroscopic and
computed tomography procedures (data from the
U.K. 1998)
37
With reference to procedures (XI)
  • The most appropriate projection should be
    adopted, from the patient protection point of
    view, when the diagnostic information so allows.
  • For pregnant women, PA abdominal projections are
    preferable to minimize uterus dose
  • For skull examinations eye lenses are better
    protected in PA projection

38
With reference to procedures (XII)
  • The smallest film and cassette size compatible
    with the expected image must be used together
    with automatic collimation. Otherwise the patient
    would be over-irradiated, by receiving radiation
    over a larger volume and transversal surface, and
    the raise in scattered radiation would reduce the
    image quality and increase the operating
    personnel doses.
  • When using equipment without automatic X Ray beam
    collimation, it should be verified that the
    radiation field is reduced up to the smallest
    size compatible with the required image, even in
    fluoroscopy applications (the unit usually will
    allow for radiation field reductions both in
    radiography as in fluoroscopy).

39
With reference to procedures (XIII)
  • The use of the anti-scatter grid improves the
    image quality, but ALWAYS increases patient
    doses. It is advisable to evaluate whether the
    grid is actually necessary in equipment where its
    use is optional according to procedure (e.g.
    mammography) or patient characteristics. In that
    case, one should check its location (some grids
    imply an increase in patient skin irradiation up
    to factors 2, 3 or even higher)
  • When the grid is of a focussed type, it is
    important to confirm that the focus-film distance
    has been selected within the correct range

40
With reference to procedures (XIV)
  • When a change of the usual technique is needed in
    order to improve or maintain the image quality -
    without changing any element of the imaging
    device - it is advisable to check the performance
    of the whole imaging chain. Usually, the change
    implies an increase in patient dose.
  • The patient should be visible from the operation
    control panel.
  • When possible the fluoroscopy should be used in
    intermittent mode, irradiating the patient only
    when strictly necessary.

41
With reference to procedures (XV)
  • The use of fluoroscopy for centering the
    radiation field as a preliminary step of the
    radiographic image is not considered as a good
    radiological practice, so that it should be
    avoided.
  • Whenever possible a compression device (e.g.
    mammography), should be used as far as the
    patient can bear, since it reduces dose while
    improving image quality.

42
With reference to procedures (XVI)
  • In general radiology, the patient-tube distance
    should be as long as possible, and the
    patient-image device (detector) distance as short
    as possible (except for air gap scatter reduction
    technique)
  • In general radiology using fluoroscopy the
    patient-tube distance is usually determined by
    the collimator, which also operates as beam
    pointer, and the patient-intensifier distance
    should be as short as possible.

43
With reference to procedures (XVII)
  • In CT, the examinations should be done with the
    minimum possible number of slices giving the
    necessary radiological information. Increasing
    that number implies a higher irradiation over a
    larger volume, and would be equivalent to using
    large fields in conventional radiography,
    resulting in higher doses.
  • In general, the radiological examination should
    be performed with the strictly necessary number
    of images. Fluoroscopy time should be as short as
    possible, irrespective of the image support in
    use.

44
Summary
  • Practical rules to protect patients consist in
    periodic assessment of dose and image quality,
    with remedial action if needed
  • The practitioner should be aware of the influence
    on dose and image quality of technical parameters
    (field size, grid type, kV, type of projection)
  • Procedures (number of images and technical
    parameters to set) have to be established for
    each examination.

45
Where to Get More Information
  • International Basic Safety Standards for
    Protection Against Ionizing Radiation and for the
    Safety of Radiation Sources, Safety Series 115,
    IAEA, Vienna, 1996.
  • A practical guide on radiological protection and
    quality assurance in diagnostic radiology. CE,
    Value Programme, 1996. Vañó E, Gonzalez L, Maccia
    C, Padovani R. Edited by Cátedra de Física
    Médica, Facultad de Medicina, Universidad
    Complutense de Madrid, 28040 Madrid, Spain.
  • Radiological protection of the worker in medicine
    and dentistry. ICRP Publication 57, Pergamon
    Press, 1989.
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